Process for the preparation of isocyanates from acyl azides

ABSTRACT

Organic acyl azides and isocyanates are prepared from acyl halides and metal azides using acetonitrile in the reaction medium.

United States Patent m1 Coury et al.

PROCESS FOR THE PREPARATION OF ISOCYANATES FROM ACYL AZIDES Inventors: Arthur J. Coury, Minneapolis; Edger R. Rogie'r, Hopkins, both of Min'n. I

Assignee: General Mills Chemicals, Inc., Minneapolis, Minn.

Filed: Oct. 5, 1970 Appl. No.: 78,199

(1.8. CI. ..260/453 P, 260/349, 260/407, 260/453 AI; Int. Cl cov 119/04 Field of Search ..260/453 P, 349

Organic Reactions, Vol. 111, John Wiley & Sons, Inc. pp. 373-376 (1956).

Primary Examiner-Lewis Gotts Assistant Examiner-Dolph H. Torrence Attorney-Anthony A. Juettner and Gene 0. Enockson [57] ABSTRACT Organic acyl azides and isocyanates are prepared from acyl halides and metal azides using acetonitrile in the reaction medium.

9 Claims, No Drawings chloride,

PROCESS FOR THE PREPARATION OF ISOCYANATES FROM ACYL AZIDES The present invention relates to a new process for preparing organic isocyanates and acyl azides. More particularly, it relates to such a process employing ported-e.g. dimethyl formamide alone or in combination with heptane. Moreover, it is considerably less expensive than dipolar aprotic solvent systems, is readily recovered during workup and provides products of I o-octadec'enoic (petroselinic), 7-octadecenoic, 8-octadecenoic, cis-9-octadecenoic (oleic), trans-9-octadecenoic (elaidic), ll-octadecenoic'(vaccenic), l2-

high functional purity. Since the acetonitrile based system is anhydrous, side reactions which often occur in aqueous processes for preparing azides are virtually eliminated. Our new process is readily scaled up and offers convenience and flexibility in workup with good recovery of solvent and good to excellent yields of high-quality product. Any side products (including carbamoyl azide and traces-of biuret) which may form in small amounts in the process are generally readily removed by distillation of the product.

Any of a wide variety of organic acyl halides can be used 'as the starting materials in the process of the present invention. Such acyl halides may be mono, di, tri or higher in functionality although the dihalides are preferred since they yield diisocyanates which are highly useful commercially for the preparation of polyurethanes, polyureas and the like through reaction with active hydrogen containing organic compounds. Of the acyl halides the acyl chlorides are preferred due primarily to their more ready availability and/or preparation. The following are representative of various organic acyl halides which find use in our process: aliphatic acyl halides--octanoyl chloride, decanoyl l -undecanoyl chloride,- dodecanoyl chloride, palmitoyl. chloride, oleoyl chloride, stearoyl chloride, cyclohexan'e acid chloride, suberoyl chloride, sebacoyl chloride, n-decarie-l ,IO-dicarbdxylic acid dichloride, n-hexadecane-l ,l6-dicarboxylic acid dichloride, and the like;. aromatic acyl halides-'- benzoyl chloride, te'rephthaloyl chloride, isophthaloyl chloride, 1,5-naphthalene dicarboxylic acid chloride, and the like; and complex materials such as the diacid chloride of l ,1 ,3-trimethyl--carboxy-3(p-carboxyphenyl)indane, the chlorides of polymeric fat acids and the like. I

The halides of polymeric fat acids represent one preferred group of starting materials. The halogenation or chlorination of the acids can be carried out by conventional procedures using PCI, and the like. Polymeric fat acids are well known and commercially available. One method of preparation of polymeric fat acids can be seen in U. S. Pat. No. 3,157,681. The polymeric fat acids useful in preparing the starting acyl halidesare produced by polymerizing eth'ylenically unsaturated monobasic carboxylic acids having 16 to 22 carbon atoms or the lower alkyl esters thereof. The preferred aliphatic acids are the mono and polyo lefinically unsaturated 18 carbon atom acids. Representative octadecenoic acids are 4-octadecenoic, S-Octadecenoic,

octadecenoic and the like. Representative octadecadienoic acids are 9,12-octadecadienoic (linoleic), 9,11-0ctadecadienoic, 10,12-octadecadienoic,

12,15-octadecadienoic and the like. Representative octadecatrienoic acids are 9,12,15-octadecatrienoic (linolenic), 6,9 ,l2-octadecatrienoic, 9,11,13-octadecatrienoic (eleostearic), 10,12,14-octadecatriehoic (pseudo eleostearic) and the like.- A representative 18 carbon atom acid having more than three double bonds is rnoroctic acid which is indicated to be 4,8,12,15-octadecatetraienoic acid. Representative of the less preferred (not as readily available commerci'ally) acids are: 7-heXadecenoic, 9-hexadecenoic (palmitoleic), 9-eicosenoic (gadoleic), ll-eicosenoic,

6,10,14-hexadecatrienoic ('hiragonic), 4,8,l 2,l6-eicosatetraenoic, nodonic), l3-docosenoic (erucic), (c'etoleic), and the like.

The ethylenically unsaturated acids can be polymerized using known catalytic or non-catalytic polymerization techniques. With the use of heat alone, the mono-olefinic acids (or the esters thereof) are polymerized at a very slow rate while the polyolefinic acids (or the esters thereof) are polymerized at a reasonable rate. If the double bonds of the polyolefinic acids are in conjugated positions, the polymerization is more rapid than when they are in the non-conjugated positions. Clay catalysts are commonly used to accelerate the polymerization of the unsaturated acids. Lower temperatures are generally used when a catalyst is employed.

4,8 ,1 2,1 5 ,18-eicosapentanoic (timl l-docosenoic It is also preferred that the polymeric fat acids used in the preparation of the halides are hydrogenated in order to improve the color thereof. The hydrogenation is'accomplished using hydrogen under pressure in. the presence of a hydrogenation catalyst. The catalysts generally employed in such hydrogenations are Ni, Co, Pt, Pd, Rh and others of the platinum family. In general, thecatalyst is suspended on an inert carrier such as kieselguhr, commonly used with Ni, and carbon, commonly usedwith the platinum family of catalysts. j

The acetonitrile may be used in' widely varying amounts as long'as a sufficient amount-thereof is present to accelerate the reaction of the acyl halide and the metal azide. Preferably, however, the acetonitrile will bevused in-ainounts of about 10 to 300 p ercent'by weight based on the weight of the acyl halide.

The acetonitrile may be used alone or in combination with other solvents in thepreparation-of the acyl azides. When preparing aromatic isocyanates, a higher boiling decomposition medium than acetonitrile is required for-the decomposition of the aromatic acyl azide. Thus the azide I may first be formed in the acetonitrileand then the latter can be removed and a higher boiling solvent added or a higher boiling solvent can merely be added to the azide-acetonitrile solution. Additionally, a co-solvent can be added prior to the azide formation reaction and thus the aromatic isocyanate can be formed in one step.

Any of a wide variety of co-solvents may be usedin our process as described above. These solvents are preferably the aliphatic, alicyclic or aromatic hydrocarum having a sufficiently high boiling point to accommodate the decomposition of the aromatic acid azide.

The metal azides which may be employed in the production of the acyl azides and isocyanates in accordance with our invention are preferably the alkali metal and alkaline earth metal azides such as potassium azide, sodium azide, and the like. It is especially preferred to use sodium azide. The metal azide will be used in an amount at least equivalent to the equivalents of acyl halide. And it is especially preferred to use the metal azide in an amount of from more than 1 to 3 times the equivalents of acyl halide. An excess considerably accelerates the azide formation.

When an acyl is to be prepared, the reaction temperature is maintained below that temperature where significant decomposition of azide to isocyanate occurs. Preferably, the reaction temperature for acyl azide preparations in accordance with the present invention will be in the range of about to 25C. When an isocyanate is to be prepared in one step or as a second step including a co-solvent, the reaction medium will be heated to a high enough temperature to decompose the acyl azide. Preferably, decomposition temperatures in the range of about 60 to 150C. will be used. The reaction medium is also preferably mixed, such as by stirring or other agitation during the acyl azide forming reaction.

The following Examples serve to illustrate certain preferred embodiments of the invention without being limiting.

EXAMPLEI Thirty one grams (0.1 eq.) dimer acid chloride was dropped into a stirred slurry of 7.15 g. (0.11 eq.) sodium azide and 43 ml. acetonitrile which had been heated to reflux. The dimer acid chloride had the formula C1OCDCOC1 where D is the 34 carbon atom divalent hydrocarbon radical of the dimerized fat acid obtained by polymerizing, distilling and hydrogenating (in the presence of palladium) the mixture of fat acids derived from tall oil (composed of approximately 40-45% linoleic and 5055% oleic, such %s being by weight). The addition of the dimer acid chloride took 11 minutes and then refluxing (82C.) was continued for another 1 hours. The course of the reaction was followedby infrared analysis which revealed that the conversion of dimer acid chloride to dimeryl isocyanate (OCNDNCO) was complete within 2 hours. One hundred fifty ml. n-heptane was used to wash the reaction mixture into a centrifuge bottle. The mixture was centrifuged and the heptane phase was separated from the lower acetonitrile and salt phases. The heptane was removed on a rotary evaporator and there was obtained 25 g. of dimeryl isocyanate product which had a NCO of 14.6 (titration with di-n-butylamine), Cl (ionic) of 0.00 and isocyanate '(infrared) of 96.5%. The indicated analytical procedures were also used in the Examples to follow.

EXAMPLE II Thirty-one grams (0.1 eq.) of dimer acid chloride as used in Example 1, 7.15 g. (0.11 eq.) sodium azide and 3 ml. acetonitrile were added to a reaction flask and heated. At 50C. gas began to evolve and an exothermic reaction caused the temperature of the reaction mixture to rise to.98C. before subsiding. The temperature was controlled between 78-90C. for 24 hours, by which time infrared analysis revealed conversion of acid chloride to be essentially complete. The mixture was allowed to cool to room temperature and filtered. The filtrate was stripped to a constant weight on a rotary evaporator. Twenty-four grams of dimeryl isocyanate product was obtained, said product having an NCO content of 13.2% and a Cl content of 0.13%.

EXAMPLE III Example I was essentially repeated using 92.3 g. (0.30 eq.) of the dimer acid chloride, 21.5 g. (0.33 eq.) sodium azide and 250 ml.- acetonitrile. The reaction mixture was refluxed for 24 hours by which time conversion of most of the dimer acid chloride appeared to have occurred. Eighty grams of the dimeryl isocyanate product was obtained having a NCO of 13.6, C1 of 0.3 and diisocyanate of91.5.

EXAMPLE 1V Nine. hundred thirty grams (3.0 eq.) of dimer acid chloride as used in Example I was dropped into a refluxing, stirring slurry of 430 g. (6.6 eq.) sodium azide and 1250 ml. acetonitrile over a period of 30 minutes. The reaction was followed by measuring the evolution of gas and by infrared analysis. Gas evolution was vigorous during the addition, then slowed somewhat. The mixture was refluxed for 60 minutes after the addition, by which time infrared analysis revealed the complete loss of acid chloride. Two liters of n-heptane were added to the reaction mixture and the liquid phases were transferred to a separatory funnel. The salts from the reaction mixture were rinsed with heptane (1.1.) which was also added to the separatory funnel. The lower-acetonitrile phase (1,080 m1.), saturated with heptane, was removed and the acetonitrile remaining in the heptane phase was removed by azeotropic distillation (28 0 ml.). Thus 1,360 ml. acetonitrile saturated with heptane was recovered. The heptane was removed from the dimeryl isocyanate product on a rotary evaporator. There was obtained 848 g. of product having a NCO of 13.9, a C1 of 0 and a diisocyanate of 92. The crude dimeryl isocyanate product was distilled on a 2 inch ASCO wiped film still to give approximately an 87% distillate and residue having the following analyses:

Distillate I: NCO 14.4 bDiieocyanate 98 Residue fiaNCO 5.7

EXAMPLE V the tbllowinganalyses: NCO 13.9, Cl (ionic) 0.19 and %'diisocyanate'- 90. The crude product was distilled and analyzed as in Example IV.

EXAMPLE VI Example I was essentially repeated using 310 g. (1.0 eq.) of the dimer acid chloride, 143 g. (2.2 eq.) sodium azide and 313 ml. acetonitrile. After conversion of the dimer acid chloride was complete (within 1 hour), most (295 ml.) of the acetonitrile was recovered by distillation until the temperature of the reaction mixture reached 135C. Then n-heptane (1 1.) was added and the remainder of the acetonitrile saturated with heptane (9 ml.) was recovered by azeotropic distillation. The heptane solution was filtered and stripped to a constant weight on a rotary evaporator. There was obtained 298 g. of dimeryl isocyanate product which analyzed 13.8% NCO, 0.09% Cl and 92% diisocyanate.

EXAMPLE VII Example'l was essentially repeated using 93.0 g. (0.3

' eq.) of the dimer acid chloride, 43 g. (0.66 eq.) sodium azide, 100 ml. acetonitrile saturated with heptane as recovered in Example IV and 25 ml. unused acetonitrile. The conversion of dimer acid chloride'was essentially complete in 1 hour to yield 69 g. of dimeryl isocyanate product having the following analyses: NCO 13.9, Cl 0.02 and diisocyanate 92.

EXAMPLE VIII- Example I was essentially repeated using the following reactants:

Palmjtoyl chloride 27.5 g. 0.1 eq'.)

Sodi m azide 7.15 g. (0.11 eq.) Acetonitrile EXAMPLE IX Example VIII was essentially repeated using the following reactants: v

' 119.5 g. (1eq.)

71.5 g. (1.1 eq.) 150ml.

seb coyl chloride So ium azide Acetonitrile The conversion of acid chloride to isocyanate was complete within 1 to 1 1% hours. There was obtained 97 'g. of 1,8-diisocyanatooctane NCO 42.0 and .diisocyanate 98-9).

' 10 ml. acetonitrile was quickly added to a refluxing gas towards the end of the distillation. The total reaction time was 25 minutes. The reaction mixture was til- EXAMPLE x Isophthaloyl dichloride (10.2g., 0.1 eq.) dissolved in slurry of 7.15 g. (0.11 eq.) sodium azide, 20 ml.

acetonitrile and ml. n-octane. Refluxing was continued for 7 minutes and then theacetonitrile was removed by azeotropic distillation with the octane. The temperature of the reaction mixture rose from 78 to 128C. during the distillation with vigorous evolution of tered and the filtrate was stripped on a rotary evaporator to a constantweight. There was obtained 6.8 g. of

m-phenylene diisocyanate NCO 50.7).

EXAMPLE XI Benzoyl chloride (28.1 g., 0.2 eq.) was added to a stirred slurry of 14.3 g. (0.22 eq.) sodium azide and 50 ml. acetonitrile over a period of 2 minutes. The temperature was maintained below 30C. although initially it reached 35C. Stirring was continued for minutes although infrared analysis indicated that conversion of the benzoyl chloride to benzoyl azide was essentially complete within 15 minutes. The reaction mixture was filtered and the filtrate was stripped on a rotary evaporator to a constant weight. There was obtained 28.6 g. benzoyl azide which by infrared analysis contained no obvious impurities.

. EXAMPLE XII Palmitoyl chloride (27.5 g., 0.1 eq.) was addedto a mixture of 7.15 g. (0.11 eq.) sodium azide and 50 ml.

acetonitrile being cooled with an ice bath between 5-6 reaction'mixture was cooled to 15C. and was filtered and the filter cake was washed with methylene chloride. The solvents were then removed on a rotary evaporator below room temperature. There was obtained 27.6 g.-of palmitoyl azide product having a melting point of 38-40."C. andv which contained up to 22% isocyanate (infrared analysis).

In summary, the Examples show that: successful results are obtained with proportions of acetonitrile from essentially catalytic quantities to much higher amounts (Examples I-III), reaction rates are faster with large excesses of sodium azide (Examples 1V, VI and VII versus I and V); the process can'be scaled up (Examples IV and V); recovered acetonitrile, even that which is saturated with a co-solvent, can be effectively reused (Example VII); and a wide variety of isocyanates (Examples I-X) and azides (Examples XI and X11) were successfully prepared. 7

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In the process of preparing an organic isocyanate wherein an organic acyl halide is first reacted with an alkali or alkaline earth metal azide to produce an organic acyl azide and the latter is decomposed to the organic isocyanate, the improvement comprising carrying out the reaction of the organic acyl halide and the metal azide in the presence of acetonitrile in an amount sufficient to accelerate the reaction of the organic acyl halide and metal azide.

2. The process of claim 1 wherein the metal azide is sodium azide and the acetonitrile is present in an amount of 10 to 300 percent by weight based on the weight of the organic acyl halide.

3. The process of claim 2 wherein the organic acyl halide is a dimer acid chloride derived from dimerized fat acids prepared by polymerizing ethylenically unsaturated monocarboxylic acids of from 16 to 22 carbon atoms.

4. The process of claim 2 wherein the organic acyl halide is palmitoyl chloride. x

5. The process of claim 2 wherein th organic" halide is scbacoyl chloride. i 6. The process of claim 2 wherein the organic acyl halide is heptadecyl diacid chloride.

7. The process of claim 2 wherein the 'organic,acyl halide is isophthaloyl chloride. v

8. The process of claim 1 wherein the metal azide is used in an amount of from more than one to three times the equivalents of organic acyl halide.

9. The process of claim 1 wherein a co-solvent is also employed. 

2. The process of claim 1 wherein the metal azide is sodium azide and the acetonitrile is present in an amount of 10 to 300 percent by weight based on the weight of the organic acyl halide.
 3. The process of claim 2 wherein the organic acyl halide is a dimer acid chloride derived from dimerized fat acids prepared by polymerizing ethylenically unsaturated monocarboxylic acids of from 16 to 22 carbon atoms.
 4. The process of claim 2 wherein the organic acyl halide is palmitoyl chloride.
 5. The process of claim 2 wherein the organic acyl halide is sebacoyl chloride.
 6. The process of claim 2 wherein the organic acyl halide is heptadecyl diacid chloride.
 7. The process of claim 2 wherein the organic acyl halide is isophthaloyl chloride.
 8. The process of claim 1 wherein the metal azide is used in an amount of from more than one to three times the equivalents of organic acyl halide.
 9. The process of claim 1 wherein a co-solvent is also employed. 